GALLIUM

Name: Gallium (from “Gallia,” the Roman name for Gaul, France)

Symbol: Ga

Group: 13

Period: 4

Block: p

Category: Post-transition metals

Atomic number: 31

Atomic mass: 69.723 u

Electrons per shell: 2, 8, 18, 3

Electronegativity: 1.81

Density: 5.904 g/cc

Melting point: 29.76°C

Boiling point: 2204°C

Thermal conductivity: 29 W (m·K)

Electrical conductivity: 7.1 × 10^6 S/m

Magnetic order: Diamagnetic

Ordinary state: Solid

Oxidation states: +3

Hardness Mohs: 1.5

Vickers Hardness: No data

Brinell Hardness: 60 MPa

Most stable isotopes: Ga-69 (60.11%), Ga-71 (39.89%)

Discoverer: Paul-Émile Lecoq, French (1875)

Although the discovery of the metal had to wait until 1875, the existence of Gallium was predicted years earlier by the Russian chemistry genius Dmitri Mendeleev with such precision that it is chilling.

Mendeleev not only predicted the oxidation states the element could present but also its main physical characteristics (low melting point, density of the oxide and the pure metal, among others). The original name for Gallium was "eka-Aluminium" (just as Mendeleev had done with Technetium, which would not be discovered until the mid-20th century as it is radioactive, "eka-Manganese").

The Russian prodigy also stated that:

"The eka-Aluminium (which would later be named 'Gallium') would be discovered through spectrometry." He was correct even in this.

The Frenchman Paul-Émile Lecoq, sometimes known simply as Lecoq de Boisbaudran, first isolated the element in 1875 from Sphalerite samples, using the mass spectrometry method.

Gallium was an element that was discovered relatively late. Even today it is not as well-known, mainly because it is scarce and somewhat expensive. It has few uses in metallurgy, with the electronics industry being its main consumer (for semiconductors).

Gallium is a p-block metal, belonging to Group 13 of the Periodic Table (headed by Boron). Chemically, it closely resembles Aluminum more than any other metal, but given its low melting point and the fact that it forms "amalgams" (although it's not correct to call them such) with most metals, it is very reminiscent of Mercury.

Gallium's melting point is less than 30°C; however, its boiling point is relatively decent: approximately 2200°C. This makes it the element with the widest liquid-to-gas range. This is Gallium's most famous characteristic. Holding a piece of highly pure metal in the palm of your hand for a few minutes (depending on the ambient temperature) causes it to transition from solid to liquid, but it solidifies easily. This has made it a kind of "toy" for enthusiasts, much safer than Mercury, a metal it is always compared to, as unlike Mercury, Gallium is not toxic (although neither I nor anyone with minimal metallurgical knowledge recommends using it idly).

In its high-purity, solid state, it is a soft, slightly malleable, and poorly ductile metal, very soft: it can be cut with a kitchen knife.

Gallium is a corrosive agent, just as Mercury is, in the sense that when it melts, it tends to form alloys with metals that come into contact with it in its liquid phase. For this reason, it must be handled with caution. In this aspect, Gallium is arguably more dangerous than Mercury, as unlike Mercury, Gallium is capable of mixing with Iron/Steel (famous for being the exception with Mercury) and, moreover, with common glass. This means that molten Gallium can adhere to glass and dissolve part of it.

It is one of the few elements (along with Silicon, Bismuth, and the compound H₂O, water, among others) that expands upon solidifying. What does this mean? When a metal melts, the volume it occupies is usually greater. This is easy to understand if we consider that the atoms are increasingly separated from each other, expanding. With Gallium and some other elements (always isolated cases), the opposite happens: they contract upon melting. The problem with this is that if you were to pour liquid Gallium into a weak container and wait for it to cool, you would see the container burst as the Gallium expands, not contracts, upon cooling.

Incidentally, I mentioned earlier that it is capable of wetting glass. This necessitates transporting (or storing) it in plastic capsules.

Gallium (Ga), chemical element with atomic number 31, is a soft metal with unique properties, such as a low melting point (29.76 °C), which distinguishes it from other metals. In terms of corrosion resistance, metallic gallium exhibits remarkable stability in various environmental conditions, but its behavior against chemical agents is more limited than that of noble metals like gold (Au) or platinum (Pt). With a density of 5.91 g/cm³ and an abundance of ~19 ppm in the Earth's crust, gallium is relatively rare, and its chemical reactivity makes it susceptible to certain environments, although its ability to form protective layers in some cases mitigates corrosion.

Gallium is stable in dry and humid air at room temperature, forming a thin layer of gallium oxide (Ga₂O₃) that acts as a passivating barrier, protecting it from further oxidation by oxygen (O₂). In fresh and saltwater, gallium also resists corrosion for moderate periods, although in saltwater (with sodium chloride, NaCl), the formation of gallium chlorides (GaCl₃) can accelerate degradation over time, especially in the presence of electrolytes. However, gallium is vulnerable to acids and bases. Oxidizing acids, such as nitric acid (HNO₃), react rapidly and vigorously, dissolving gallium to form gallium nitrate (Ga(NO₃)₃) or other compounds. Reducing acids, such as hydrochloric acid (HCl), attack gallium more slowly, and in some cases, the formation of a passivating oxide or chloride layer can retard corrosion. Strong bases, such as sodium hydroxide (NaOH), also dissolve gallium, forming hydroxocomplexes like sodium gallate (NaGa(OH)₄).

Gallium's ease in forming compounds, especially with halogens, oxygen, and nitrogen, is a key characteristic exploited in industrial applications, such as the manufacture of semiconductors (e.g., gallium arsenide, GaAs) and alloys. Although less resistant to corrosion than noble metals, its relative stability in air and water, along with its ability to form protective layers in certain environments, makes it suitable for uses in electronics and other technologies where exposure to corrosive agents is controlled. Gallium's reactivity, combined with its low melting point, requires careful handling in aggressive chemical environments, but its chemical versatility makes it a valuable material in specialized applications.

As a metal, Gallium has few uses, and since it is expensive, it is only used when there is an express need to achieve a lower melting point in typical "White metal" or "Pot metal" alloys. These names refer to most low-melting-point alloys primarily used in large bearings, such as the famous Babbitt alloy.

Gallium mixes well with all p-block metals and the metalloid Antimony. It also forms alloys with Copper and Silver, Aluminum, etcetera, although none have major utility.

Gallium's primary use is, ironically, in its compound form: Arsenide (GaAs) and Nitride (GaN) are materials used in electronics for their properties as semiconductors, though this falls outside my field and directly into the discipline of electronics.

Undoubtedly, the most famous alloy of the metal is Galinstan (it's not correct to add an accent mark at the end, -tán, as it is a registered trademark).

Galinstan is composed of three low-melting-point elements, namely Indium, Tin, and Gallium itself. This alloy has replaced Mercury in applications where this heavy metal was formerly used, such as in thermometers.